Fabrication of organic electronic circuits by contact printing techniques

ABSTRACT

A method for fabricating an organic conductor path on a substrate includes providing a printing stamp with a hydrophobic patterned printing side that is loaded with a printing medium containing an organic conductive polymer and, by bringing it into contact with a hydrophilic substrate, a patterned layer including the organic polymer are formed on the substrate. The method can be operated continuously through selection of suitable geometries for the printing stamp and the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/DE2003/02837, filed Aug. 25,2003, and titled “Fabrication of Organic Electronic Circuits by ContactPrinting Techniques,” which claims priority under 35 U.S.C. §119 toGerman Application No. DE 102 40 105.5, filed on Aug. 30, 2002, andtitled “Fabrication of Organic Electronic Circuits by Contact PrintingTechniques,” the entire contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to a method for fabricating an organic conductorpath on a substrate.

BACKGROUND

In conventional semiconductor technology based on inorganicsemiconductors, a period of several months is generally required inorder to fabricate first patterns of the corresponding chips from acircuit design. These comparatively long periods of time are caused, inpart, by the multiplicity of very complicated production stepscomprising a wide variety of methods such as photolithography,deposition etching processes and the like that are involved whenprogressing through the fabrication of the microchip.

For specific applications, conductive organic polymers are appropriatein the long term as an alternative to the inorganic semiconductormaterials that have been used heretofore. Organic layer systems can beapplied to a substrate in a relatively uncomplicated manner by means ofsuitable printing techniques. In contrast to microelectronic componentsbased on inorganic semiconductors, structures made of organic conductivematerials can be fabricated comparatively cost-effectively.

However, the task of patterning the conductive material in accordancewith the circuit logic to be obtained is still required for organiclayer systems. If polymer layers are deposited onto a substrate, thereare in principle the possibilities of either patterning the polymerlayer after deposition, defining individual regions on the substrate ina targeted manner prior to deposition, or controlling the deposition ofthe polymer onto the substrate in a defined manner. The last-mentionedpossibility affords the advantage of saving material costs andcomplicated cleaning or recovery processes.

If the polymer layer is intended to be patterned only after deposition,then it is possible, by way of example, to incorporate suitablephotoactive components into the polymer and to generate a polymer havingphotoactive properties in this way. Through selective exposure, it isthen possible, by way of example, to alter the solubility of the polymerin a developer in a targeted manner.

As an alternative, it is also possible to apply a photoresist layer tothe polymer layer, which photoresist layer is initially selectivelyexposed with the aid of a photomask in order to prepare for apatterning. After the development of the photoresist layer, a mask isobtained, and the uncovered sections of the polymer are removed in asubsequent etching step, in most cases a plasma process. Finally, thephotomask also has to be removed, e.g. by means of a suitable solvent.

A considerable disadvantage of this method is the need for a costlyphotolithographic process step. Besides high material and apparatuscosts for the provision of the photomasks, photomask exposers,photoresists, developer solutions and solvents, in some instancesspecial wastes that can only be disposed of with a high outlay alsoarise during production. Moreover, the technique of photolithographyonly permits a limited number of substrate elements to be patterned in asingle production cycle, corresponding outage times for preparation andfollow-up measures likewise having to be taken into consideration, whichlead to a low process throughput.

In addition to optical methods for selective exposure using photomasks,it is also possible to use mechanical methods for patterning. Thus, byway of example, the screen printing method affords the possibility ofapplying a patterned resist layer to the polymer. Analogously to theoptical methods, this method likewise requires a structure transferprocess for transferring the resist layer onto the substrate in anetching process and the subsequent removal of the resist. In comparisonwith the optical methods, however, the structure resolution that can beachieved is only approximately 200 μm and can therefore only be used forproducing relatively coarse structures. It is thus sufficient forimaging large-area interconnects and electrodes but has to be replacedby higher-resolution methods in the case of finer structures, such aslarge scale integrated circuits.

Inkjet printing is also a mechanical method for producing definedstructures in polymer layers. In this case, the polymer is sprayed ontothe substrate surface as a solution in the form of small droplets. Thisrequires the polymer either itself to be present in a printableconstitution or to be correspondingly prepared by admixture of suitablesolvents and additives. The additives and solvents should rapidlyevaporate after application in order to prevent the layer structure fromrunning together.

A method is disclosed in Sirringhaus, H, Kawese, T. Friend, R.H.:High-Resolution Ink-Jet Printing of All-Polymer Transistor Circuits, inMRS Bulletin (July 2001), in which a template is used to define theregions to be printed on the substrate surface. The template comprisesfine polyimide structures which are not wetted by the polymer printingink and thus serve as a structure base in the subsequent inkjetprinting.

However, the inkjet method has a series of disadvantages. The polyimidestructures initially have to be patterned by photolithographic methods,resulting in high costs being incurred. In addition, dispensing with theuse of polyimide structures leads to a reduction of the resolution as aresult of the printing structure running together. As a furtherdisadvantage, the inkjet method permits only a line-by-line structureconstruction, thereby causing a low throughput rate and hence highprocess costs.

Consequently, while the high resolutions of photolithographic patterningtechniques are associated with high costs, the less expensive screenprinting or inkjet methods permit only a low resolution.

SUMMARY OF THE INVENTION

In light of the above, it is an object of the invention to provide acost-effective method for patterning polymer films made of electricallyconductive organic polymers which further enables a high resolution evenof small structures.

This and other objects are achieved in accordance with the presentinvention by implementing a method for fabricating an organic conductorpath on a substrate, comprising least the following steps: providing asubstrate; providing a printing stamp with a patterned printing sidesituated thereon, the patterned printing side having elevated sectionsand deeper sections arranged between the elevated sections and whichcorrespond to a structure to be imaged; loading of the patternedprinting side with a printing medium containing at least one conductiveorganic polymer or a precursor of such a polymer; if appropriate,removing excess printing medium from the elevated sections of thepatterned printing side, so that the printing medium remains only in thedeeper sections of the patterned printing side; mutual arranging andaligning of the substrate and the printing stamp with respect to oneanother, the substrate being arranged on the patterned printing side,and bringing the patterned printing side into contact with thesubstrate; and removing the printing stamp from the substrate andtransferring the printing medium situated in the patterned printing sideonto the substrate.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of specific embodiments thereof,particularly when taken in conjunction with the accompanying drawingswhere like numerals designate like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F depict a schematic illustration of a sequence of a printingoperation in accordance with the present invention.

FIGS. 2A and 2B depict a schematic illustration of reinforcing ahydrophilic/hydrophobic contrast by application of a hydrophobic silanelayer in accordance with the present invention.

FIG. 3 depicts a schematic illustration of a printing operation in acontinuous method with a roller technique in accordance with the presentinvention.

FIG. 4 is a diagram illustrating a family of characteristic curves of anorganic transistor fabricated according to Example 17 (width 40 μm,length 100 μm).

FIG. 5 is a diagram illustrating a family of characteristic curves of anorganic transistor fabricated according to Example 18 (width 20 μm,length 100 μm).

DETAILED DESCRIPTION

The present invention provides a very simple and cost-effective methodfor producing structures made of a conductive polymer on a substrate. Incontrast to time- and cost-intensive photolithographic methods, hardlyany residues of materials and chemicals used are obtained during themethod. A complex preparation of substrate, photoresist, exposure maskand exposure apparatus is not necessary and the method can also becarried out continuously given corresponding geometry of substrate andprinting stamp, with the result that it is possible to achieve highturnover at low cost.

The achievable resolution is also extremely satisfactory for a methodbased on mechanical processes for applications in microelectronics anddistinctly surpasses the resolution that can be achieved with comparablemechanical methods such as inkjet printing or screen printing.

In accordance with the present invention, a method for fabricating anorganic conductor path on a substrate includes the steps of: providing asubstrate; providing a printing stamp with a patterned printing sidesituated thereon, the patterned printing side having elevated sectionsand deeper sections arranged between the elevated sections and whichcorrespond to a structure to be imaged; loading of the patternedprinting side with a printing medium (a printing medium) containing atleast one conductive organic polymer or a precursor of such a polymer;if appropriate, removing excess printing medium from the elevatedsections of the patterned printing side, so that the printing mediumremains only in the deeper sections of the patterned printing side;mutual arranging and aligning of the substrate and the printing stampwith respect to one another, the substrate being arranged on thepatterned printing side, and bringing the patterned printing side intocontact with the substrate; and removing the printing stamp from thesubstrate and transferring the printing medium situated in the patternedprinting side onto the substrate.

In an advantageous embodiment of the method according to the invention,the printing solution transferred onto the substrate is fixed by abaking step. The elevated temperature during the baking step means thatsolvent residues can evaporate, so that only the constituents dissolvedin the printing medium remain and the desired structure composed of saidconstituents is solidified and fixed on the substrate. Moreover,particularly at the beginning of solvent evaporation, the removal ofsolvent increases the viscosity of the printing solution, therebypreventing the solution from running together after the printing processand stabilizing the imaged structure directly after application.

It is advantageous to provide the patterned printing side with ahydrophobic interface and the substrate a hydrophilic interface. Theopposing interface properties of the patterned printing side andsubstrate facilitate stripping the printing medium from the patternedprinting side and transferring the latter onto the substrate surface.This ensures that the substantially complete transfer of the printingmedium from the patterned printing side onto the substrate is achieved.No residues of the printing medium that may cause defective structureimaging remain in the deeper sections of the printing stamp. At the sametime, the speed at which the printing solution is transferred isoptimized in the case of opposing interface properties, with the resultthat a higher turnover of structures formed can be achieved.

The contrast in interface properties between patterned printing side(hydrophobic) and substrate (hydrophilic) can be achieved by producingthe patterned printing stamp from a hydrophobic material (e.g.hydrophobic polymers such as polybenzoxazoles, polyimides, novolaks,etc.) and the substrate from an oxidic material (e.g. glass or ceramic)or a metal (e.g. copper or nickel). In addition, polymers containinghydroxyl groups (e.g. polyvinylpyrrolidone) or else polymers that aresubsequently functionalized with hydroxyl groups, for example bytreatment in oxygen plasma, are also suitable for the fabrication of thesubstrate.

It is particularly advantageous to provide a printing solution that ishydrophilic. Similar interface properties of substrate and printingsolution (in this case a hydrophilic nature) facilitate the adhesion ofthe printing solution to the substrate. The comparable interactionbetween the molecules of the printing solution and the molecules of thesubstrate surface in comparison with the interactions between substratemolecules and printing solution molecules among one another furthermorebrings about a stabilization of the printed-on structure since theprinting structure is largely prevented from running apart and thusbeing destroyed. Moreover, the stripping of the printing medium from thepatterned printing side is facilitated by the opposing interfaceproperties and situations in which the printing solution remains in thedepressions of the patterned printing form are counteracted by thecapillary forces present. Furthermore, a hydrophilic nature of theprinting solution results in a large surface tension with respect to air(hydrophobic), as a result of which the structure of the printing mediumapplied to the substrate is stabilized by the formation of a largecontact angle at the edge regions of the structure.

Printing suspensions may also be used as an alternative to printingsolutions. When using a printing suspension, it is necessary to takeaccount of a substantially homogeneous distribution and dispersion ofthe suspended particles (e.g. organic conductive polymers as carriers ofelectrical conductivity) in the dispersion medium in order to achieve auniform distribution of the particles in the structure produced and thusa reproducible behavior of a resultant electronic circuit structure thatis formed. As used herein, the term “printing medium” refers to a mediumcomposed of one or both of a printing solution and a printingsuspension.

In an advantageous embodiment of the invention, the hydrophobicinterface of the patterned printing side and, respectively, thehydrophilic interface of the substrate are produced by an interfacetreatment. An interface treatment extends the number of materials thatcan be used in practicing the invention since the interface can bemodified largely independently of the bulk properties. By means ofcorresponding treatments, it is often possible for the interfaceproperties to be better optimized (i.e. for example set to a specificsurface tension value) than would be possible just through pure materialselection. In this way, it is also possible to achieve, when required, areversal of the interface properties from hydrophilic to hydrophobic,and vice versa. Thus, for example, a hydrophilization can be achieved bymeans of an oxidative treatment with introduction of hydroxyl groups,amine groups or thiol groups, while a hydrophobization of a hydrophilicsurface can be achieved using the reactive surface atoms by bindingmonofunctional compounds with hydrophobic alkyl radicals. In this case,the surface treatment, for increasing the hydrophilic/hydrophobiccontrast, may be achieved by application of a dilute solution of thecorresponding hydrophobizing reagent and evaporation of the solvent orapplication of the reagent from the gas phase. This opens up thepossibility of using hydrophilic materials that are originally to beused as substrates also as materials for the printing stamp providedwith a hydrophobic printing side, and vice versa.

The printing stamp preferably has a cylindrical geometry, the patternedprinting side being arranged on the circumferential area thereof. It ispossible to realize a continuous method in this way, the printing stampin the form of a roller, roll or drum being brought into contact withthe substrate. Continuous methods have the advantage of enabling fasterproduction cycles since the dead times that occur in discontinuousmethods and serve to prepare for a subsequent production cycle areomitted. As a result, the turnover rate is increased and betterproduction capacity utilization is achieved, as a result of which theproduction costs can be reduced overall.

It is advantageous for the patterned printing side and/or the printingstamp to be composed of a flexible material. Flexible materials permitbetter contact-making between printing stamp and substrate sinceirregularities of the surfaces involved (e.g. unevennesses orcontaminating particles that have been introduced) are compensated forgiven a corresponding contact pressure. As a result, the structuretransfer quality is improved and the error rate is reduced.

It is particularly advantageous for the substrate to be composed of aflexible material. In addition to the advantageous effect on theprinting quality already mentioned, a continuous method can be realizedin the case of flexible substrate materials, for example by the use of asubstrate film that is continuously brought into contact with a printingstamp shaped as a roll.

In a preferred embodiment of the present invention, a pressure roller isprovided, to force the flexible substrate against the patterned printingside so as to facilitate transfer of the printing solution to thesubstrate. In particular, a continuous method can be utilized asdescribed below, in which the flexible substrate can be pressed onto thepatterned printing side with a sufficiently high contact pressure,thereby improving the transfer quality.

The method can be applied to the same substrate a number of times withidentical or different printing sides with respectively identical ordifferent printing solutions. Particularly in the case of highly complexelectronic circuits, a complex three-dimensionally patterned arrangementof circuits is present which is formed formally from stackingtwo-dimensional circuit planes one above the other. In this case, it isalso necessary to vary the conductivity of the materials used in orderto be able to realize a wide variety of electronic components. Suchcontact systems can be fabricated by repeated application of the methodaccording to the invention with different printing solutions andstructures.

The conductor path is-preferably supplemented to form a microelectroniccomponent. It may only be necessary to fabricate partial regions of amicroelectronic component with the aid of the method according to theinvention, while the remaining portion can be produced by conventionalmethods. This results in high flexibility in the selection of passablecomponents to be realized whilst adhering to economic aspects, since theindividual methods may require different costs.

The microelectronic component is preferably a field-effect transistor.Field-effect transistors are components that are often used inmicroelectronics on account of their diverse possibilities for use,comprise various structure planes and can be fabricated cost-effectivelyby the method according to the invention in a multistage method.

FIGS. 1A-1F illustrate the individual steps of an exemplary embodimentof a printing method in accordance with the present invention. Referringto FIG. 1A, a printing stamp is first provided including a carriersubstrate 2 and a patterned printing side 1 arranged on the carriersubstrate 2, where the printing side 1 includes a structure profile inthe form of a positive structure.

In the next step depicted in FIG. 1B, the patterned printing side 1 isloaded with a polymer solution 3 or a polymer suspension containing aconductive polymer, where the recessed sections of the patternedprinting side 1 are sufficiently covered with the printing solution orsuspension 3. In this step, it is not essential that the elevatedsections of the patterned printing side 1 come into contact with theprinting medium 3. However, as can be seen in FIG. 1B, excess printingmedium 3 is situated on the elevated sections of the printing side 1.

As shown in FIG. 1C, the excess printing medium 5 situated on theelevated sections of the patterned printing side 1 is removed by beingstripped away mechanically with the aid of a squeegee device 4, so thatonly a defined volume of printing medium 6 remains in the deeper orrecessed sections of the patterned printing side 1. After removal of theexcess printing medium, the printing stamp is rotated 180°, as shown inFIG. 1D, with the printing medium 6 remaining in the structure of thepatterned printing side 1 due to adhesion and capillary interaction, andis aligned in a suitable manner above a substrate 7. By lowering theprinting stamp and/or raising the substrate 7, the patterned printingside 1 is brought into contact with the substrate 7. The patternedprinting side 1 of the printing stamp is then released from thesubstrate 7 by raising the printing stamp and/or lowering the substrate,while the printing medium 8 is maintained on (i.e., is released from therecesses of the printing side 1) and thus defines a layered structurefor the substrate 7 as shown in FIG. 1E. A small amount of organicconductive polymer may remain in the deep recess sections of thepatterned printing side 1 on account of the surface tension.

The substrate 7 is then subjected to a baking process, where solvent isevaporated from the substrate and the layered structure is fixed andbecomes a solidified layer structure 9 on the substrate 7 as shown inFIG. 1F.

The method for forming a circuit as described above and depicted inFIGS. 1A-1F can be modified, as depicted in FIG. 2A, by providing ahydrophobized patterned printing side 1 on a carrier substrate 2 forincreasing the hydrophilic/hydrophobic contrast at the surface and thusenhance the separation of the printing medium from the printing side inorder to facilitate transfer of the printing medium to the substrate. Ahydrophobic silane layer 10 is applied completely on the deeper andelevated sections of the patterned printing side 1. In addition, thepatterned printing side 1 may be isolated, as shown in FIG. 2B, ratherthan situated on a carrier substrate 2 as shown in FIG. 2A.

FIG. 3 schematically depicts how the method of the invention is carriedout in a continuous manner. A rotating roll 13 acts as a printing stamp,where a patterned printing side (not shown) is arranged on thecircumferential area of the roll. A specific region of the roll dipsinto a reservoir trough 12 containing the printing medium 3, so that thedipping region is loaded with the printing medium 3. A squeegee device 4that just touches the elevated sections of the patterned printing sidestrips excess printing medium 3 away from the elevated sections of thepatterned printing side, which flows back into the trough. A flexiblefilm 11 serves as a substrate, and is pressed onto the circumferentialarea of the rotating roll 3 with the aid of a rotating pressure roller14. By virtue of the opposite direction of rotation of roll 13 andpressure roller 14, the substrate film 11 is guided through betweenthese two rollers and, upon making contact with the patterned printingside arranged on the circumferential area of the rotating roll 13,accepts the printing medium 3 situated in the deeper sections of thepatterned printing side in the form of the desired structure profile.The method is carried out continuously by providing a continuous supplyof substrate film 11 as well as printing medium 3 within the reservoirtrough 12.

The following examples demonstrate the formation of printing stamps andcircuits utilizing the methods of the present invention.

EXAMPLE 1 Fabrication of a Planar Masterplate (Photoresist)

A 1.3 μm thick layer of a positive photoresist is applied to a round4-inch glass wafer, which serves as a printing stamp, by spin coating.The photoresist is dried for one minute at 100° C. in order to evaporatethe solvent. The structures to be transferred are subsequently imaged byexposure utilizing a dark field mask. The latent image of the structuresare developed to form elevated and deeper sections and the glass waferis dried in vacuo in order to drive out the solvents. The deepersections of the developed structures have a depth of 1.3 μm.

EXAMPLE 2 Fabrication of a Planar Printing Stamp Made of Polybenzoxazole

A layer of a poly-o-hydroxylamine (20% by weight in NMP) is applied ashydrophilic material to a round 4-inch glass wafer, which serves as aprinting stamp, by spin coating. The poly-o-hydroxylamine is synthesizedfrom isophthalic acid dichloride and 3,3′-dihydroxybenzidine 1:1(polybenzoxazole precursor). Afterward, a baking step is carried out for2 minutes at 120° C. in order to evaporate the solvents, followed by aheat treatment step for 2 hours at 400° C. for the purpose of cyclizingpolybenzoxazole (PBO).

A layer of a positive photoresist is applied to the polybenzoxazolelayer obtained by spin coating. The photoresist is dried for 1 minute at100° C. and subsequently exposed through a dark field mask that imagesthe structures to be transferred. The structures are developed to formthe patterned printing side and dried at 100° C. to leave photoresiststructures that form the etching mask for the subsequent step of etchingthe polybenzoxazole. Using an oxygen plasma, the polybenzoxazole isetched and the structure profile is transferred.

The residual photoresist is subsequently removed using acetone and thenthe glass substrate is rinsed with water and dried. The layerthicknesses of the polybenzoxazole layer and thus the depth of thereservoir are set by way of the spinning speed and formulation of thepoly-o-hydroxyamine. For example, at a rotational speed of 2000 rpm (30s), the polybenzoxazole layer thickness will be 2.5 μm; for a rotationalspeed 3000 of rpm (30 s), the polybenzoxazole layer thickness will be1.8 μm; and for a rotational speed of 4000 rpm (30 s), thepolybenzoxazole layer thickness will be 1.3 μm.

EXAMPLE 3 Fabrication of a Planar Printing Stamp Made of Polyimide

A layer of poly-(biphenyl-3,340 -4,4′-tetracarboxylicdianhydride-co-1,4-phenylenediamine) (10% by weight in NMP) is appliedto a round 4-inch glass substrate, which serves as a printing stamp, byspin coating. The cyclization to give the polyimide (PI) is achieved bycarrying out a subsequent baking step for 10 minutes at 120° C. in orderto evaporate solvents and a heat treatment step for 2 hours at 400° C. Alayer of a positive photoresist is applied to the polyimide layer (spincoating). The photoresist is dried for 1 minute at 100° C. andsubsequently exposed through a dark field mask that images thestructures to be transferred. The structures are developed and dried at100° C. The residual photoresist structures form the etching mask forthe subsequent step of etching the polyimide. The polyimide is etched byoxygen plasma, resulting in the formation of the structure profile.Finally, the residual photoresist is removed using acetone and the glasssubstrate is rinsed with water and dried.

The layer thicknesses of the polyimide layer and thus the depth of thereservoir can be set by varying the spinning speed. For example, for arotational speed 2000 rpm (30 s), the polyimide layer thickness will be1.9 μm; for a rotational speed 3000 rpm (30 s), the polyimide layerthickness will be 1.4 μm; and for a rotational speed 4000 rpm (30 s),the polyimide layer thickness will be 1.1 μm.

EXAMPLE 4 Fabrication of a Flexible Printing Stamp By Means of aPhotoresist

A 1.3 μm thick layer of a positive photoresist is applied to apolyethylene naphthalate film (PEN) by spin coating. In order toevaporate the solvent, the positive photoresist is dried for 1 minute at100° C. and subsequently exposed through a dark field mask that imagesthe structures to be transferred. The structures are developed to formthe structure profile including elevated and recessed sections, and thehydrophobic polyethylene naphthalate film is dried in vacuo. Thedeveloped structures form the reservoir for the polymer suspension witha depth of 1.3 μm. Finally, the polyethylene naphthalate film isadhesively bonded onto a round plastic cylinder that serves as aprinting stamp.

EXAMPLE 5 Fabrication of a Flexible Printing Stamp Made of Polyimide

A layer of a positive photoresist is applied to a polyimide film(Kapton®) by spin coating. In order to remove solvents, the photoresistis dried for 1 minute at 100° C. and is subsequently exposed through adark field mask that images the structures to be transferred. Thestructures are developed and dried at 100° C. The residual photoresiststructures form the etching mask for the subsequent step of etching thepolyimide. The polyimide is etched by means of oxygen plasma, therebyfashioning the structure profile. The depth of the reservoir structurecan be determined by varying the etching time and also the etching rate.In the subsequent step, the residual photoresist is removed usingacetone. The hydrophobic polyimide film is subsequently adhesivelybonded onto a round plastic cylinder that serves as a printing stamp.

EXAMPLE 6 Hydrophobic Coating of a Printing Stamp

Octadecyltrichlorosilane (OTS) is vapor-deposited on the printing stampsdescribed in Examples 1 to 5 and in a vacuum furnace at a temperature of100° C. and a pressure of 200 mbar. The octadecyl group introduceshydrophobic properties into the system, while the trichlorosilane groupis used for binding to the substrate, the chloride ions serving asleaving groups. In order to ensure sufficient hydrophobization, thevapor deposition time is about 1 hour. Besides hydrophobization from thegas phase, the hydrophobization may also be effected from solution bydipping into a 0.5% dry hexane solution.

EXAMPLE 7 Loading of a Planar Printing Stamp with a Polymer Suspension

The printing stamps described in Examples 1 to 3 are coated with apolymer suspension, containing PEDOT:PSS in a BaytronP® formulationcommercially available from Bayer AG (Germany), by a spin coating methodfor 15 seconds at a rotational speed of 2000 revolutions per minute. Theexcess polymer suspension is stripped away with the aid of a siliconesqueegee.

EXAMPLE 8 Loading of a Planar Printing Stamp with a Polymer Suspension

The printing stamps described in examples 1 to 3 are dipped into apolymer suspension containing PEDOT:PSS in a BaytronP® formulation. Theexcess polymer suspension is stripped away with the aid of a siliconesqueegee.

EXAMPLE 9 Loading of a Flexible Printing Stamp with a Polymer Suspension

The printing stamps described in Examples 4 and 5 are dipped into apolymer suspension containing PEDOT:PSS in a BaytronP® formulation. Theexcess polymer suspension is stripped away with the aid of a siliconesqueegee.

EXAMPLE 10 Transfer of the Polymer Suspension to an Si/SiO₂ Wafer

Each of the loaded printing stamps described in Examples 7 and 8 isfixed with a sample holder in such a way that the active surface withthe patterned printing side is oriented downward. A substrate to beprinted is a silicon wafer with a silicon dioxide layer formed bythermal oxidation. The substrate is brought into contact with thepolymer suspension for 60 seconds by raising and pressing the substrateto the sample holder, which fixes the substrate to the sample holder bysuction in a predetermined position.

EXAMPLE 11 Transfer of the Polymer Suspension to Glass Substrates

Each of the loaded printing stamps described in Examples 7 and 8 isfixed with a sample holder in such a way that the active surface withthe patterned printing side is oriented downward. A glass plate to beprinted is then brought into contact with the polymer suspension for 60seconds by raising and pressing the substrate to the sample holder,which fixes the substrate by suction by suction in a predeterminedposition.

EXAMPLE 12 Transfer of the Polymer Suspension to Polymer Films

Each of the loaded printing stamps described in Examples 7 and 8 isfixed with a sample holder in such a way that the active surface withthe patterned printing side is oriented downward. A polymer film to beprinted is subsequently fixed on a planar carrier and brought intocontact with the polymer suspension for 60 seconds by raising andpressing the polymer film to the sample holder, which fixes thesubstrate carrier by suction in a predetermined position.

EXAMPLE 13 Aligned Transfer of the Polymer Suspension

The transfer of the polymer suspension to the printing stamp is achievedin a similar manner as described in Examples 10 to 12, with a differencebeing that the substrate to be printed is first provided with apatterned layer according to a suitable method. Different orientationsof a printing stamp are detected with the aid of a microscope on thebasis of alignment marks provided in the layout of the respectiveprinting stamp. In addition, the substrate holder has free mobility, sothat the substrate holder is moved to a predetermined position to be ina selected alignment with the printing stamp based upon the orientationof the alignment marks.

EXAMPLE 14 Thermal Fixing of the Polymer Structures

Substrates that have been pretreated in accordance with Examples 10 to14 are released from contact with their printing stamps and dried for 1minute at a temperature of 100° C. and then for 2 minutes at atemperature of 120° C. on a hot plate.

EXAMPLE 15 Direct Thermal Fixing of the Polymer Structures

Substrates that have been pretreated according to Examples 10 to 14 areheated to a temperature of 80° C. while maintaining contact with theirprinting stamps. In this example, the heat transfer is effected via aheatable substrate holder. Afterward, the substrate is dried for 1minute at a temperature of 100° C. and then for 2 minutes at atemperature of 120° C. on a hot plate.

EXAMPLE 16 Printing with Flexible Printing Stamps

In this example, the printing stamp described in example 9 is a plasticcylinder. The plastic cylinder is rolled over a polyethylene naphthalatefilm whose surface has been activated beforehand by treatment with anoxygen plasma. For this purpose, the polyethylene naphthalate film ispressed onto the roll-type printing stamp by a second roll heated to atemperature of 70° C. In this case, the travel speed of the polyethylenenaphthalate film is 0.2 cm/s. Afterward, the printed film section istransferred to a furnace and dried at a temperature of 120° for theperiod of 5 minutes under a protective gas atmosphere.

EXAMPLE 17 Electrical Characterization in the Case of a MonolayerPrinting

A highly doped, thermally oxidized silicon wafer printed according tothe method described in example 15 is provided as a substrate, where theprinted-on structures correspond with a simple construction of anorganic field-effect transistor (OFET), and the printed-on PEDOT:PSSstructures correspond to the source and drain elements of thefield-effect transistor. Pentacene is vapor-deposited as an organicconductive material onto these structures at a temperature of 60° C.Transistors having a charge carrier mobility of 0.03 cm²/V-s at athreshold voltage of 16 V and a subthreshold voltage gradient of 3.4 Vper decade given an on/off current ratio of 10³ were obtained in thisexample. The corresponding characteristic curve is illustrated in FIG.4.

EXAMPLE 18 Electrical Characterization in the Case of an AlignedMultilayer Printing

A glass substrate is printed with a layer of PEDOT:PSS as described inExample 15, where the printed-on structures form a layer of an organicfield-effect transistor that contains gate elements. The gatedielectric, which includes 10% poly-4-hydroxystyrene, 1% crosslinker and89% n-butanol, is subsequently applied by means of spin coating. Thecoating by the spin coating method is carried out at a rotational speedof 2000 revolutions per minute for a period of 30 seconds. This isfollowed by drying at a temperature of 100° C. for 1 minute and,finally, the crosslinking process for the period of 2 minutes at atemperature of 200° C. on a hot plate.

The layers containing the source and drain elements are printedaccording to the method described in Example 13. Pentacene isvapor-deposited as an organic conductor onto the structures produced inthis way, at a temperature of 60° C. Transistors having a charge carriermobility of 0.05 cm²/V-s, a threshold voltage of 20 V and a subthresholdvoltage gradient of 9 V per decade given an on/off current ratio of 100were obtained in this example. The corresponding characteristic curve ofthe transistor is illustrated in FIG. 5.

EXAMPLE 19 Multiple Use of the Printing Stamps

The printing stamps fabricated in Examples 2, 3 and 5 can be usedrepeatedly. In this example, prior to reuse, it is necessary to carryout cleaning in order to remove the residual polymer suspension. Thecleaning is achieved in an ultrasonic bath containing acetone as asolvent for a period of 2 minutes. Afterward, the printing stamp isrinsed with water and dried. A renewed hydrophobization of the patternedprinting side as described in Example 6 is necessary only after everyfifth use or after a number of weeks when the printing stamp has notbeen used.

As noted above, FIG. 4 shows the family of characteristic curves of anorganic transistor fabricated according to Example 17, where the currentintensity at the drain contact (drain current, in μA) is plotted againstthe applied voltage between drain and source contacts (drain-sourcevoltage, in V). The family parameter is the voltage applied between gateand source electrodes (gate-source voltage). The organic transistorfabricated has a width of 40 μm and length of 100 μm. From the curvesplotted in FIG. 4, it is possible to discern a significant increase inthe drain current as the drain-source voltage rises. This dependenceincreases as the gate-source voltage rises.

As noted above, FIG. 5 shows the family of characteristic curves of anorganic transistor fabricated according to Example 18, where the currentintensity at the drain contact (drain current, in μA) is plotted againstthe applied voltage between drain and source contacts (drain-sourcevoltage, in V). The family parameter is the voltage applied between gateand source electrodes (gate-source voltage). The organic transistorfabricated has a width of 20 μm and a length of 100 μm. In this example,as in Example 17, it is possible to discern a significant increase inthe drain current as the drain-source voltage rises. This dependenceincreases as the gate-source voltage rises.

Comparison of FIGS. 4 and 5 makes it clear that the dependence betweendrain current and drain-source voltage increases as the width of thetransistor decreases given the same gate-source voltage, as ischaracteristic of a field-effect transistor. Thus, an organicfield-effect transistor fabricated in accordance with the methods of thepresent invention includes the same features as a conventionalfield-effect transistor produced from an organic semiconductor.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. Accordingly, it is intendedthat the present invention covers the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents.

List of Reference Symbols

-   1 patterned printing side-   2 carrier substrate-   3 printing medium-   4 squeegee device-   5 excess printing medium-   6 defined volume of the printing medium in deeper sections of the    patterned printing side-   7 substrate-   8 printing medium with a defined layer structure-   9 solidified layer structure-   10 hydrophobic silane layer-   11 flexible film-   12 reservoir trough-   13 rotating printing stamp-   14 pressure roller

1. A method for fabricating an organic conductor path on a substrate,comprising: (a) providing a substrate; providing a printing stamp with apatterned printing side situated thereon, the patterned printing sideincluding elevated sections and recessed sections arranged between theelevated sections that correspond to a structure to be imaged; (b)loading of the patterned printing side with a printing medium containingat least one conductive organic polymer or a precursor thereof; (c)removing any excess printing medium from the elevated sections of thepatterned printing side such that the printing medium remains only inthe recessed sections of the patterned printing side; (d) mutuallyarranging and aligning the substrate and the patterned printing side ofthe printing stamp with respect to each other and bringing the patternedprinting side into contact with the substrate; and (e) removing theprinting stamp from the substrate so as to transfer the printing mediumsituated in the patterned printing side onto the substrate, wherein thepatterned printing side includes a hydrophobic interface, the substrateincludes a hydrophilic interface and the printing medium is hydrophilic.2. The method of claim 1, further comprising: (f) upon transferring theprinting medium to the substrate in step (e), baking the substrate toaffix the printing medium to the substrate.
 3. The method of claim 1,wherein at least one of the patterned printing side and the printingstamp comprises a flexible material.
 4. The method of claim 1, whereinthe substrate comprises a flexible material.
 5. The method of claim 4,wherein the patterned printing side is brought into contact with thesubstrate by pressing the flexible material of the substrate against thepatterned printing side with a pressure roller.
 6. The method of claim1, further comprising: (f) repeating steps (a)-(e) a plurality of timesto transfer a plurality of printing mediums to the substrate.
 7. Themethod of claim 6, wherein different printing sides are utilized in atleast two series of repeating steps (a)-(e).
 8. The method of claim 7,wherein the conductor path formed on the substrate by repeating steps(a)-(e) comprises a field-effect transistor.
 9. The method of claim 6,wherein different printing mediums are utilized in at least two seriesof repeating steps (a)-(e).
 10. The method of claim 1, wherein theconductor path formed on the substrate comprises a microelectroniccomponent.
 11. The method of claim 9, wherein the microelectroniccomponent comprises a field-effect transistor.